Recently, high-intensity LED products featuring high luminance emission and entailing substantial heat release are commercially marketed. Besides use as backlight units in liquid crystal displays and mobile phones, LED products now find widespread use as general illuminations and the like. WO 2009/154260 discloses an encapsulating material having heat resistance, photostability and weather resistance in which an epoxy-containing silicone is added to a phenyl-containing silicone resin for improving adherence. WO 2007/100445 discloses that a silicone resin composition comprising a phenyl-containing resin and a linear phenyl-containing hydrogen-oligoorganosiloxane is useful in prolonging the lifetime of LED.
Commonly used as LED packages are leadframes in the form of copper plates having silver electroplated thereon. It is known that if silicone resin-encapsulated LED is held under sulfur releasing service conditions, a blackening problem that the silver surface discolors to black due to formation of silver sulfide occurs because the silicone resin is gas permeable. Blackening of leadframes causes a lowering of LED luminance. The encapsulant resins are thus required to be low gas permeable. Although the aforementioned silicone resins have light resistance, thermal discoloration resistance, and impact resistance, a discoloration phenomenon still occurs in a sulfide test on a phenyl-containing silicone resin which is improved in adherence by adding epoxy groups or the like, or a reliable resin resulting from a combination of a phenyl-containing resin with a linear phenyl-containing hydrogen oligoorganosiloxane. This is true even when the phenyl-containing silicone resin which is considered low gas permeable among silicone resins is used.